Japanese Patent Application Publication No. 2011-203298 discloses a developing device including a cartridge frame for accommodating therein developing agent, a developing roller, a seal having a side seal member for sealing an axial end portion of the developing roller, and a blade unit having a layer thickness regulation blade for regulating a thickness of a layer of the developing agent carried on a peripheral surface of the developing roller.
The cartridge frame has a support surface formed with a fixing hole for fixing a longitudinal end portion of the blade unit by a thread threadingly engaged with the fixing hole. The support surface is positioned outward of an inner edge of the side seal member in the longitudinal direction of the blade unit. That is, the support surface is positioned outward of the blade unit in the longitudinal direction thereof.